Rechargeable batteries, typically lithium-ion batteries, are widely used in consumer electronic devices, especially portable computers and mobile devices. Although examples of devices with which such batteries may be used are manifold, some recent examples include smartphone, notebook, tablet, and netbook computing devices, or the like, which have a CPU and memory that require operating power. When the device is not powered by the battery, an adapter is commonly used to power the device with which the battery is associated. At the same time, the adapter provides power to a charging circuit in the device to charge the battery. In such charging circuits, a synchronous switching buck converter is often used to control the charging current to the battery, while providing a substantially constant voltage to the load.
Traditionally, when the power required by the CPU and system load increase to reach the adapter power limit, the charge current can be reduced to zero, thereby giving a higher priority to power the system than to charge the battery. However, in certain conditions, if the CPU power demands are greater than those that can be met by the adapter, the adapter may crash. An example of such condition is when the system is cold and the CPU power needed for application processing and speeding up data flow is much more than the power that the adapter can supply, even with zero charging current.
In the past, several solutions to the problem have been advanced. For example, one solution disables the CPU high current mode. This, however, lowers the system performance. Another solution uses an adapter with an increased current capability. This, however, increase the adapter cost. Yet another solution reduces the system bus voltage. This, however, is not a widely adopted battery charger solution, and is not suitable for a high power system. Still another solution is to add an additional boost converter and include a boost controller. This, however, requires at least a power MOSFET, diode, and other circuit components. The cost of this solution is high and needs more space.
Thus, in order to solve the problem of operating a CPU at a high speed to improve the system performance, while not crashing the adapter, it has been suggested to use the battery and adapter to simultaneously power the system when power demands are high. One way in which this has been done has been to use a boost converter in the charging circuit to convert the battery power for delivery to the system. The charger can operate in a synchronous buck mode during the battery charging and in a boost mode when additional power to CPU and system is needed. This type of charging circuit is referred to herein as a “hybrid power battery charger.”
Because the adapter current is well controlled by the hybrid power battery charger, the battery discharging current changes when total system current changes. However, for any particular portable device, numerous battery pack options may be available. For example, numerous interchangeable battery pack designs may be used. For example, 3S1P (3 cells in series 1 cell in parallel), 3S2P, 3S3P, and so on can be used to power the same device. However, different battery packs have different discharging current capabilities. Thus, for the same device, different power delivery capabilities may be available, depending on the particular battery pack design that is selected or installed.
Each battery pack generally has an over-current protection circuit to protect the battery in the event the load attempts to draw current above a maximum current level that is established for the battery. For example, usually, the over-current protection circuits turn off a built-in MOSFET device in series with the battery output, if the current drawn from the battery is over the maximum current level. In normal operation, it is preferred that this kind of protection should never be triggered.
What is needed, therefore, is a system and method of the type that uses the battery charger in a boost mode to boost the current available from the battery to supplement the adapter current when needed, and that controls the discharge rate of the battery when it is connected in this mode.